High luminance blue LED and white LED which have been recently developed have come to find wide applications in backlights for display boards, full color displays and cellular phones, etc. As the sealing materials for photoelectric transducers such as LED, a heat-curable resin composition containing an epoxy-containing compound and an acid anhydride curing agent has been conventionally used because of its excellent colorless transparency. As the curing agent for epoxy-containing compound used in sealing photoelectric transducers, alicyclic acid anhydrides such as methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride and tetrahydrophthalic anhydride have been generally used. Among such anhydrides, methylhexahydrophthalic anhydride and methyltetrahydrophthalic anhydride which are liquid at ordinary temperatures have been mainly used because of their easiness of handling.
As the production method for the cyclohexanetricarboxylic anhydride, there have been proposed a method in which trimellitic acid is hydrogenated by molecular hydrogen in a polar solvent in the presence of a rhodium catalyst supported on activated carbon having a specific surface area of 940 m2/g or more, and then, cis,cis-1,2,4-cyclohexanetricarboxylic acid which is obtained by recrystallization from tetrahydrofuran and/or acetonitrile solvent is converted into an anhydride by using an anhydrizing agent such as acetic anhydride (Patent Document 1), and a method in which an alkyl trimellitate is nuclear-hydrogenated into an alkyl 1,2,4-cyclohexanetricarboxylate under heating in the presence of a noble metal-containing hydrogenation catalyst and an aliphatic alcohol, the resultant ester is hydrolyzed in sulfolane and/or dimethyl sulfoxide solvent, and then the obtained 1,2,4-cyclohexanetricarboxylic acid is cyclized by anhydrization (Patent Document 2). However, the cyclohexanetricarboxylic anhydrides obtained in the proposed methods are all solid.
Since the cyclohexanetricarboxylic anhydride produced by known methods is solid and therefore hard to handle, such an anhydride is often used after being dissolved in a solvent. This makes the operation complicated and requires a drying step which can cause the pollution of environment in some cases.
It has been expected that the cyclohexanetricarboxylic anhydride will find many applications such as sealing resins for photosemiconductors because of its excellent colorless transparency. However, the solid nature of the known cyclohexanetricarboxylic anhydride makes its handling difficult to limit the application.
[Patent Document 1] U.S. Pat. No. 5,412,108
[Patent Document 2] JP 8-325196A